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Date:   Wed, 6 May 2020 15:27:02 +0530
From:   Amit Kucheria <amit.kucheria@...durent.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>, Lukasz Luba <lukasz.luba@....com>,
        Rob Herring <robh+dt@...nel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/4] dt-bindings: thermal: Add the idle cooling device

On Wed, Apr 29, 2020 at 4:07 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> Some devices are not able to cool down by reducing their voltage /
> frequency because it could be not available or the system does not
> allow voltage scaling. In this configuration, it is not possible to
> use this strategy and the idle injection cooling device can be used
> instead.
>
> One idle cooling device is now present for the CPU as implemented by
> the combination of the idle injection framework belonging to the power
> capping framework and the thermal cooling device. The missing part is
> the DT binding providing a way to describe how the cooling device will
> work on the system.
>
> A first iteration was done by making the cooling device to point to
> the idle state. Unfortunately it does not make sense because it would
> need to duplicate the idle state description for each CPU in order to
> have a different phandle and make the thermal internal framework
> happy.
>
> It was proposed to add an cooling-cells to <3>, unfortunately the
> thermal framework is expecting a value of <2> as stated by the
> documentation and it is not possible from the cooling device generic
> code to loop this third value to the back end cooling device.
>
> Another proposal was to add a child 'thermal-idle' node as the SCMI
> does. This approach allows to have a self-contained configuration for
> the idle cooling device without colliding with the cpufreq cooling
> device which is based on the CPU node. In addition, it allows to have
> the cpufreq cooling device and the idle cooling device to co-exist
> together as shown in the example.
>
> Reviewed-by: Rob Herring <robh@...nel.org>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>


Reviewed-by: Amit Kucheria <amit.kucheria@...aro.org>


> ---
>  - V4:
>    - Added Rob Herring reviewed-by
>  - V3:
>    - Removed extra line with tab inside
>  - V2:
>    - Fixed comment type
>    - Added dual license
>    - Fixed description s/begins to/should/
>    - Changed name s/duration/duration-us/
>    - Changed name s/latency/exit-latency-us/
>    - Removed types for latency / duration
>    - Fixed s/idle-thermal/thermal-idle/
> ---
>  .../bindings/thermal/thermal-idle.yaml        | 145 ++++++++++++++++++
>  1 file changed, 145 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/thermal/thermal-idle.yaml
>
> diff --git a/Documentation/devicetree/bindings/thermal/thermal-idle.yaml b/Documentation/devicetree/bindings/thermal/thermal-idle.yaml
> new file mode 100644
> index 000000000000..7a922f540934
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/thermal/thermal-idle.yaml
> @@ -0,0 +1,145 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +# Copyright 2020 Linaro Ltd.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/thermal/thermal-idle.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Thermal idle cooling device binding
> +
> +maintainers:
> +  - Daniel Lezcano <daniel.lezcano@...aro.org>
> +
> +description: |
> +  The thermal idle cooling device allows the system to passively
> +  mitigate the temperature on the device by injecting idle cycles,
> +  forcing it to cool down.
> +
> +  This binding describes the thermal idle node.
> +
> +properties:
> +   $nodename:
> +     const: thermal-idle
> +     description: |
> +        A thermal-idle node describes the idle cooling device properties to
> +        cool down efficiently the attached thermal zone.
> +
> +   '#cooling-cells':
> +      const: 2
> +      description: |
> +         Must be 2, in order to specify minimum and maximum cooling state used in
> +         the cooling-maps reference. The first cell is the minimum cooling state
> +         and the second cell is the maximum cooling state requested.
> +
> +   duration-us:
> +      description: |
> +         The idle duration in microsecond the device should cool down.
> +
> +   exit-latency-us:
> +      description: |
> +         The exit latency constraint in microsecond for the injected
> +         idle state for the device. It is the latency constraint to
> +         apply when selecting an idle state from among all the present
> +         ones.
> +
> +required:
> +  - '#cooling-cells'
> +
> +examples:
> +  - |
> +    #include <dt-bindings/thermal/thermal.h>
> +
> +    // Example: Combining idle cooling device on big CPUs with cpufreq cooling device
> +    cpus {
> +            #address-cells = <2>;
> +            #size-cells = <0>;
> +
> +            /* ... */
> +
> +                 cpu_b0: cpu@100 {
> +                         device_type = "cpu";
> +                         compatible = "arm,cortex-a72";
> +                         reg = <0x0 0x100>;
> +                         enable-method = "psci";
> +                         capacity-dmips-mhz = <1024>;
> +                         dynamic-power-coefficient = <436>;
> +                         #cooling-cells = <2>; /* min followed by max */
> +                         cpu-idle-states = <&CPU_SLEEP &CLUSTER_SLEEP>;
> +                         thermal-idle {
> +                                 #cooling-cells = <2>;
> +                                 duration-us = <10000>;
> +                                 exit-latency-us = <500>;
> +                         };
> +                };
> +
> +                cpu_b1: cpu@101 {
> +                        device_type = "cpu";
> +                        compatible = "arm,cortex-a72";
> +                        reg = <0x0 0x101>;
> +                        enable-method = "psci";
> +                        capacity-dmips-mhz = <1024>;
> +                        dynamic-power-coefficient = <436>;
> +                        #cooling-cells = <2>; /* min followed by max */
> +                        cpu-idle-states = <&CPU_SLEEP &CLUSTER_SLEEP>;
> +                        thermal-idle {
> +                                #cooling-cells = <2>;
> +                                duration-us = <10000>;
> +                                exit-latency-us = <500>;
> +                        };
> +                 };
> +
> +          /* ... */
> +
> +    };
> +
> +    /* ... */
> +
> +    thermal_zones {
> +         cpu_thermal: cpu {
> +                polling-delay-passive = <100>;
> +                polling-delay = <1000>;
> +
> +                /* ... */
> +
> +                trips {
> +                        cpu_alert0: cpu_alert0 {
> +                                    temperature = <65000>;
> +                                    hysteresis = <2000>;
> +                                    type = "passive";
> +                        };
> +
> +                        cpu_alert1: cpu_alert1 {
> +                                    temperature = <70000>;
> +                                    hysteresis = <2000>;
> +                                    type = "passive";
> +                        };
> +
> +                        cpu_alert2: cpu_alert2 {
> +                                    temperature = <75000>;
> +                                    hysteresis = <2000>;
> +                                    type = "passive";
> +                        };
> +
> +                        cpu_crit: cpu_crit {
> +                                    temperature = <95000>;
> +                                    hysteresis = <2000>;
> +                                    type = "critical";
> +                        };
> +                };
> +
> +                cooling-maps {
> +                        map0 {
> +                             trip = <&cpu_alert1>;
> +                             cooling-device = <&{/cpus/cpu@.../thermal-idle} 0 15 >,
> +                                              <&{/cpus/cpu@.../thermal-idle} 0 15>;
> +                        };
> +
> +                        map1 {
> +                             trip = <&cpu_alert2>;
> +                             cooling-device =
> +                                        <&cpu_b0 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>,
> +                                        <&cpu_b1 THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
> +                       };
> +                };
> +          };
> +    };
> --
> 2.17.1
>

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